Obesity and overweight have reached world-wide epidemic proportions. Further, overweight and obesity are highly correlated with the incidence of high blood pressure and high cholesterol. The United Nations has identified three of the world's top ten health risks as obesity, high blood pressure and high cholesterol. Globally, there are more than one billion overweight adults and at least 300 million of these overweight adults are considered obese. In the United States alone, over 60% of the population is considered overweight or obese. In addition, overweight is one of the fastest growing disorders among children. The incidence of childhood overweight is approaching levels of one in three, resulting in over 22 million children under age 5 being overweight in Europe and North America alone.
Besides being recognized as a disease in its own right, obesity is also associated with such life-threatening diseases as high blood pressure, diabetes, coronary artery disease, congestive heart failure, stroke, osteoarthritis, various cancers and reproductive health and psychological disorders. In 1998, the United States alone had economic losses of over $92 billion due to overweight and obesity. Further, there is no doubt that obesity increases mortality because of its pathophysiologic effects.
Overweight and/or obesity can be empirically determined by calculation of either the Body Mass Index (BMI) or the lean body mass. The BMI is the product of the weight (in kilograms) of an individual divided by the height (in meters) squared. For adults, a BMI of 25 or more is considered overweight and a BMI of 30 or more is considered obese. Lean body weight is the total body weight minus the weight of the adipose or fat component. Typically, men are considered overweight when they have a fat content of about 24 percent or more and women 30 percent or more. Lean body weight, therefore represents the sum of a persons bones, muscles and organs. Lean body weight can be calculated using empirical formulas and objectively using dual-energy X-ray absorptiometry (DEXA). DEXA determines the body weight contribution of the lean soft tissue, fat soft tissue and bone compartments by differentiating between the tissue attenuation of two different X-ray wave lengths.
The major factor responsible for the increase in overweight and obesity appears to be environmental or cultural rather than hereditary. However, adopted children tend to have weight problems more like their biological parents than their adoptive parents, indicating that genetics plays at least a minor role. Obesity and overweight tends to run in families, most likely resulting from shared lifestyle and eating habits. Children of obese or overweight parents have a 25 to 30% chance of becoming obese themselves. However, the current epidemic of overweight and obesity is ample evidence that genetics may actually be reinforcing an environmental problem. Thus, family background, whether environmental or genetic, is predictive of a tendency or risk of becoming overweight or obese.
Critical life periods also are correlated to weight gain. For men, the critical periods are between 35 and 40 years, after marriage and after retirement. For women the critical periods occur during adolescence, after marriage, during pregnancy, during menopause and after retirement. In women, the problem of weight gain is further exacerbated by the fact that women tend to have less lean body mass. Lean body mass is more metabolically active than fat soft tissue. Consequently, women have less ability to burn excess calories than men. Generally, men have higher rates of overweight while women have higher rates of obesity.
In women, the effects of overweight or obesity may have even more serious health consequences during menopause. For example, women approaching menopause are at an increased risk of heart disease and osteoporosis, weight gain and urinary incontinence. During menopause, if a woman is more than 30% overweight, she is at an increased risk of heart disease. The risk of heart disease and urinary incontinence can be reduced by decreasing body fat while the risk of osteoporosis can be treated by a variety of methods, including hormone replacement therapy (HRT), bisphosphonates and selective estrogen receptor modulators (SERMs). Pharmacologic treatments directed to preventing or ameliorating osteoporosis may have serious side effects, including cardiovascular disease, increased blood pressure and an increased risk of breast cancer, and do not address the tendency for weight gain and its associated risks.
There are a wide variety of techniques and methods advocated to treat obesity and overweight. Current weight control methods range from surgical intervention, to diet modification, to acute reductions in caloric intake, to pharmacologic or naturopathic remedies, both of which are designed to increase metabolism and/or suppress the appetite. Each of these methods has its deficiencies. For example, surgical methods to reduce the intake of food include stapling the stomach or reducing the length of the small intestine. While such surgical methods are generally effective, they are limited to the morbidly obese because of the risk of serious and/or fatal complications.
A more obvious approach to weight loss is altering dietary habits. While it is generally conceded that weight loss will result from consuming less calories than expended, such methods do not appear to be a viable solution for the legions of overweight. Therefore, a large number of special diets are advocated to facilitate weight loss. For example, some individuals use diets that focus on shifting calories between food groups, such as high protein/low carbohydrate diets or grapefruit diets. Some individuals resort to fad or crash diets or acute reductions in food consumption. Unfortunately, the rapid decrease in body weight without adequate nutritional intake may have a boomerang effect resulting in increased obesity, as well as physiologic repercussions, such as acidosis or ketosis, that occasionally results in death or other serious complications. Further, while a variety of appetite suppressants are espoused, many of them do not work and some may be fatal. For example, phen-fen, a combination of fenfluramine and phentermine, was found to cause fatal heart valve damage only after it had become a widely used dietary supplement.
Methods of decreasing overweight or obesity that focus on rapidly decreasing caloric intake may also be counter-productive. While decreased food intake is an effective method of losing weight, the energy stored in fat cells is generally the last energy store utilized by the body. Generally, the first energy stores liberated result in glucose metabolism and the second result in protein metabolism. Because glucose stores are relatively small, the result of a restricted diet without enough exercise to maintain muscle mass is the mobilization of energy stored in the protein compartment. Because lean body mass has a much higher metabolic rate than does adipose tissue, and because adipose tissue is initially spared during times of fast, diets that restrict caloric intake often result in a decrease in lean body mass before any energy derived from the fat compartment is utilized. Thus, the abrupt decrease in caloric intake may have the ironic effect of lowering lean body mass, lowering total metabolic rate and decreasing the mobilization of fat stores. The result is that while a decrease in total body weight may be achieved, the weight reduction comes at the expense of the lean body component rather than the fat component, effectively increasing the individual's percent body fat.